#include <iomanip>
#include <iostream>
using namespace std;

const int kMaxN = 666;

double f[kMaxN][kMaxN];

int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int n;

  cin >> n;
  n /= 2;
  for (int i = 2; i <= n; i++) {
    f[0][i] = f[i][0] = 1.0f;
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      f[i][j] = 0.5 * (f[i - 1][j] + f[i][j - 1]);
    }
  }
  cout << fixed << setprecision(4) << f[n][n] << "\n";
  return 0;
}